1. Field of the Invention
This invention relates to railroad braking systems and, more particularly, to air distribution manifolds configured to retrofit existing passenger rail car pneumatic braking systems for electronic braking control.
2. Description of Prior Art
Brake systems for railroad passenger cars are commonly operated and controlled by air. Such pneumatic brake systems typically include operator controls, a control airline, dual chamber air tanks having primary control reservoirs and emergency control reservoirs, AB valves with pipe brackets and service/emergency portions, and brake application devices. The control airline extends over the entire length of the train and operatively connects with the AB valves of the individual passenger rail cars, and each AB valve operatively connects with the brake applications system of the corresponding car.
When the engineer operates the controls to brake the train under ordinary conditions, air pressure in the control airline decreases which in turn causes air from the primary control reservoirs of each car to enter the AB valves and activate the braking systems of each car. The operator controls determine the pressure drop in the control airline, and the pressure drop in the control airline determines the braking pressure applied by the braking device. The greater the pressure drop in the control airline, the more braking pressure applied by the braking devices.
In the event of a sudden, substantial pressure drop (in excess of 20 psi) in the control airline, air from the emergency reservoirs and the primary reservoirs of each car enter the AB valves causing the braking devices to apply full braking pressure. This condition can occur, for example, when a car is disconnected from the remainder of the train venting the pressure in the control airline.
While these braking systems effectively brake trains, several undesirable things occur during operation of these braking systems. For example, when the engineer operates the controls to brake the train, the pressure drop in the control airline propagates from the front to the rear of the train at the speed of sound. Therefore, each railroad car begins to brake just after the car in front of it. This creates a "run-in" condition during which cars run into the cars immediately in front of them. Another problem is that the same braking force is applied to all of the cars irrespective of their individual weights. Thus, an empty car will slow more quickly than a full car thereby increasing the occurrences and severity of run-in conditions. In extreme cases, the wheels of the car can lock, potentially leading to derailment. Run-in conditions are also intensified in longer trains.
To solve the problems encountered in these braking systems, electronically controlled barking systems have been proposed in which wired electronic or wireless signals from the engine are transmitted to respective receivers in the cars. Because the signal is transmitted at the speed of light in these systems, the run-in problem is substantially eliminated. Further, onboard, individualized, electronic control can be provided for each car in connection with electronically controlled braking systems. Thus, anti-skid systems, such as the anti-skid system disclosed by U.S. Pat. No. 5,735,580 to Klink, which is hereby fully incorporated herein by reference, are utilized to appropriately vary the braking force applied to individual cars based on the weight of the individual cars.
Unfortunately, prior art electronic braking systems do not operate with conventional passenger rail car pneumatic braking systems and are not capable of adapting conventional passenger rail car pneumatic braking systems to electronic control. As a result, every passenger car of a train must be electronically equipped, making conversion economically impractical. U.S. Pat. Nos. 5,335,974 and 5,813,730 to Klink, which are hereby fully incorporated herein by reference, provide an apparatus for retrofitting freight cars with electronic braking controls. However, these devices fail to address the complexity of and redundance designed into passenger railcars.